Dual stroke length mechanism



Dec. 9, 1969 E, BE NARSKI 3,482,458

DUAL STROKE LENGTH MECHANISM Filed July 16, 1968 3 Sheets-Sheet 1 INVENTOR THADDEUS E. BEDNARSKI ATTORNEY 1386- 9, 1969 T. E. BEDNARSKI DUAL STROKE LENGTH MECHANISM 3 Sheets-Sheet 2 Filed July 16, 1968 FIG. 3A

FIG. 3F

INVENTOR THADDEUS E. BEDNARSKi ATTORNEY Dec. 9, 1969 T. E. BEDNARSKI 3,482,458

DUAL STROKE LENGTH MECHANISM Filed July 16, 1968 3 Sheets-Sheet :5

'ET'IIIA ni- 4| INVENTOR THADDEUS E. BEDNARSKI ATTORNEY United States Patent O 3,482,458 DUAL STROKE LENGTH MECHANISM Thaddeus E. Bednarski, Timonium, Md., assiguor to The Black and Decker Manufacturing Company, Towson, Md., a corporation of Maryland Filed July 16, 1968, Ser. No. 745,164

Int. Cl. F16h 21/22 U.S. Cl. 74-44 14 Claims ABSTRACT OF THE DISCLOSURE SUMMARY OF THE INVENTION The present invention is directed to an efficient, novel, simple, inexpensive and reliable motion transmission mechanism adapted for use in, for example, a powered reciprocating sabre saw. The transmission includes a rotatable input and a reciprocating output and is adapted to deliver a different stroke length and different speed to the output depending upon the direction of rotation of the input. In a motor powered sabre saw, this provides two different blade stroke lengths and speeds by reversing the motor and allows the motor to run at full capacity at all times. Main objects of the present invention, therefore, are to provide a novel rotation to reciprocation motion transmission device adapted to deliver different output amplitudes and speeds in response to a different directional input, which device employs a minimum of parts, requires a minimum of space and minimizes the stresses on the various parts.

Further objects are to provide a novel device of the above character which is adapted for use in a variety of installations such as, for example, a motor powered reciprocating sabre saw, which minimizes the size, weight and cost of the installation and makes full use of the motor capacity at all times.

Additional objects of the invention are to provide a novel transmission device of the above character which is relatively inexpensive to manufacture, rugged in construction and reliable in use.

Other objects and advantages of the present invention will become more apparent from a consideration of the detailed description to follow taken in conjunction with the drawings annexed hereto.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a view partly in elevation and partly in section illustrating a portable, power operated sabre saw embodying a preferred form of the present invention;

FIG. 2 is a bottom plan view of a portion of FIG. 1 looking in the direction of the arrows 22;

FIGS. 3A-3C are sequential schematic illustrations of the positions of parts of the inventive motion transmission during rotation of the motor in one direction;

FIGS. 3D-3F are views similar to FIGS. 3A-3C during rotation of the motor in the other direction;

FIG. 4 is a fragmentary view, similar to FIG. 1, illustrating a modified form of the invention;

FIG. 5 is a bottom plan view of a portion of FIG. 4 looking in the direction of the arrows 55;

FIG. 6 is a sectional view of FIG. 4 taken along the line 66 thereof;

FIG. 7 is a somewhat schematic, plan view illustration of still another modified form of the present invention;

FIG. 8 is a view, similar to FIG. 7, but showing the position of the parts for rotation of the motor in the opposite direction; and

FIG. 9 is a sectional view of FIG. 7 taken along the line 9-9 thereof.

BROAD STATEMENT OF THE INVENTION Broadly described, the present invention relates to a motion transmission device comprising a first member reversely rotatable about a first axis, a second member pivotally interrelated with said first member and a third member for movement relative thereto about second and third axis, respectively, said first axis being spaced from said second and third axes, means guiding at least a portion of said third member remote from said third axis for reciprocating movement, cooperable abutment means on said first and second members limiting pivotal movement of said second member relative to said first member, whereby said second member is movable relative to said first member from a first position to a second position, said second member being adapted to pivot to and remain in said first position when said first member rotates in one direction and to pivot to and remain in said second position when said first member rotates in a second direction, whereby said portion of said third member undergoes reciprocational movement having different a mplitudes and speeds for rotational movement of said first member in said first and second direction.

In another aspect, the invention relates to a reciprocating saw mechanism comprising a housing having a reversible electric motor therein, rotatable means driven by said motor, slide rneans supported by said housing for longitudinal reciprocating movement and adapted to have a saw blade secured thereto, linkage means within said housing and interconnecting said rotatable means and said slide means, said linkage means being constructed and interconnected with said rotatable means and said slide means whereby to reciprocate said slide means through strokes of different amplitude and speed for forward and reverse motor operation, respectively.

DETAILED DESCRIPTION Referring now more specifically to the drawings, a portable, power operated sabre saw, which is one installation in which the present invention finds particular use, is illus- 3 trated generally at 11 in FIG. 1. However, it is to be understood that this is illustrative only and the present invention finds more general use in devices having a reciprocating output (linear or otherwise) and wherein two different output stroke amplitudes and/or speeds are desirable.

With this in mind, the saw 11 is seen to include a motor housing 13 and a gear case 15 secured together by screws 17. An electric motor (not shown) is disposed within the housing 13 and is powered from a suitable electric source connected thereto by a line cord 18. A handle 19 is secured to the housing 13 and gear case 15 and is provided with an on-otf switch 21 and a reversing switch 23 to control the motor.

The motor has an output shaft 25 which extends into the gear case 15 and is supported by a bearing 27. The end of the shaft 25 has pinion teeth 29 formed thereon drivingly engaging a gear 31 which forms the input to a novel transmission 32. A bearing 33 rotatably supports the gear 31 and both are held in place upon the gear case 15 by a fastener 35. A crank pin 37 is pressed into the gear 31 radially of its rotational axis and has one end of a crank 39 pivotally connected thereto. The other end of the crank 39 is pivoted by a pin 43 to one end of a connecting rod 41 forming the output of the transmission 32.

The other end of the connecting rod 41, in turn, is pivoted by a pin 45 to a slide 47 which is guided for reciprocating movement longitudinally of the gear case 15 by clam-shell bearings 49, 51. To mount the bearings 49, 51, the gear case 15 has a pair of downwardly facing split, annular bosses 53, 55 which receive lateral projecting portions 57, 59 respectively, on the bearings 49, 51 to position them longitudinally and laterally of the gear case 15. A cover plate 61 secured by screws 63 to the gear case 15 holds the bearing 49, 51 in place on the bosses 53, 55 and facilitates easy assembly and disassembly of the other parts within the gear case.

The bearings 49, 51 preferably are formed from a material having a relatively low coeflicient of friction and are generally channel shaped so that when assembled, they define a passageway 65 in which the slide 47 is disposed. The sides of each of the bearings 49, 51 are cut away along a portion of their length to accommodate lateral movement of the connecting rod 41 and each of the bearings 49, 51 is grooved to accommodate reciprocatory movement of the pin 45. Further details on the bearings,49, 51 together with their assembly to the gear case 15 may be obtained from the copending application of Leonard Alshruhe, Ser. No. 764,202, filed Oct. 1, 1968 and owned by the assignee of the present application.

The forward end of the slide 47 has a clamp 67 thereon to which a saw blade 69 may be fixed by means of a set screw 71. The blade 69 extends beyond the gear case 15 and thorugh a shoe 73 mounted thereon and reciprocates when the motor is energized. A resilient seal 75 is positioned around the slide 47 adjacent the forward end of the bearings 49, 51 to prevent chips, sawdust and other foreign matter from being drawn into the bearings 49, 51 by the reciprocating slide 47.

It will be appreciated that it is desirable in many installations to vary the stroke length and/or the lineal speed of the reciprocating slide 47. For example, it is desirable to be able to vary the stroke length and lineal speed of the slide 47 in the saw 11 disclosed herein to obtain different cutting strokes and speeds for the saw blade 69. Thus, a relatively slow blade speed is desirable in starting a cut and in cutting tight curves while a relatively fast blade speed is advantageous for straight cutting and where accuracy is not a prime requisite.

In regard to the cutting stroke length, a long stroke is desirable, where space permits, in order to present more teeth to the material being cut. This is so since it enhances blade life (less wear per tooth) and because there is better heat distribution along the blade. However, space requirements sometimes dictates a shorter blade stroke.

To satisfy the requirement of different blade speeds, reciprocating saws in the past have embodied solid state, variable speed controls such as is disclosed in the Gawron Patent No. 3,209,228, issued Sept. 28, 1965, as well as two-speed motor controls such as is disclosed in the Godfrey et al. Patent No. 3,155,128 issued Nov. 3, 1964. While these controls provide different blade lineal speeds, at lower blade speeds the motor is running only at a fraction of its capacity. Thus, in these devices the motor capacity (together with its size and cost) must be selected so that its output is adequate at fractional speeds. In addition, solid state variable switches are relatively expensive and contribute significantly to the total cost of the device.

Other representative prior art includes, in the area of varying the stroke of a reciprocating blade, the patents to Bradley, No. 1,035,524, and .Swanson, No. 2,890,682. Bradley employs an adjustable wobble plate arrangement to vary the blade stroke while Swanson teaches an adjustable stroke, piston-type motor. Again, each of these constructions achieves their intended function; however, in a device such as Bradley, relatively high frictional forces are developed between the wobble plate and the follower blocks during use. This, in turn, produces the problems of wear, heat and noise, and eventually leads to part failure. In a Swanson type device, a source of pressure fluid is required but is not always readily available.

Finally, the patent to Venable, No. 2,153,030, issued Apr. 4, 1939, discloses an adjustable stroke drive for a feed mechanism. This device includes a drive motor adapted to rotate a crank which is pivoted to an orbiting circular plate. A strap or sheath surrounds the plate and is connected by a connecting rod to the reciprocating feeder. The stroke of the feeder is adjustable by reversing the drive motor which, in turn, shifts the circular plate relative to the axis of the crank. This eifects a change in the radius of the orbital path of the circular plate and therefore varies the stroke of the feeder. However, it will be appreciated that the circular plate must turn within the strap causing relatively high frictional forces and both the plate and strap follow an orbital path during use of the device causing relatively high inertia forces to be developed.

The present invention discloses a novel transmission mechanism which provides two different speeds and different length strokes to a reciprocating output and has the advantages of being relatively simple and inexpensive, has no sliding parts and minimizes the mass of orbiting parts. In addition, the present invention is compact, positive and reliable in operation, and makes full use of the drive motor capacity throughout all phases of operation.

Thus, as seen in FIGS. 1 and 2, the crank 39 is limited, in its pivotal movement relative to the gear 31, by a pair of abutment pins 75, 77. When the motor shaft 25 turns in one direction, i.e. clockwise as seen in FIG. 2, the gear 31 turns counterclockwise and causes the crank 39 to pivot on the pin 37 and engage the pin 75 as shown. Then, as the gear 31 rotates, the crank 39 causes the slide 47 to reciprocate through a path defined by twice the radius from the axis of the gear 31 to the pin 43. When the shaft rotates in the other direction, i.e. counterclockwise, the gear 31 turns clockwise and the crank 39 pivots to a point where it engages the abutment pin 77. Again, the slide 47 reciprocates through a stroke defined by the radius from the axis of the gear 31 to the pin 43. Now, however, the pin 43 is closer to the gear axis (by virtue of the closer positioning of the pin 77 relative to this axis) so that the stroke of the slide 47 is shorter. In addition, the crank 39 may be notched, as shown at 76, to receive the pin 75 thereby allowing greater latitude in designing the mechanism for different length strokes.

The operation of the mechanism is better seen in FIGS. 3A-3F. FIGS. 3A-3C show the position of the parts when the gear 31 turns in a counterclockwise direction. The crank 39 rests against the pin 75 and the stroke 8, of the slide 47 is defined as twice the radius R from the axis of the gear 31 to the pin 43. During rotation of the gear 31 in the clockwise direction, the position of the part is as shown in FIGS. 3R-3F. Here, the stroke 5 of the slide 47 is defined as twice the radius R from the axis of the gear 31 to the pin 43. In this illustration, S is greater than It will be appreciated that of the transmission components, the gear 31 rotates, the crank 39 orbits, the connecting rod 41 reciprocates and pivots and the slide 47 reciprocates. None of these parts slide relative to one another so that frictional forces are minimized. In addition, since only the crank 39 undergoes orbital movement, vibrational forces developed during operation also are minimized. Also, the amplitude of slide reciprocation (and its speed) are not limited by the size of the gear 31 since, as shown, the connection between the crank 39 and connecting rod 41 can fall outside the gear 31.

Furthermore, and of significant importance, is the fact that the drive motor runs at full capacity in either the forward or reverse direction, regardless of which stroke is selected. The short stroke 5;; (and the lineal speed associated therewith) may be selected to correspond to the stroke (and speed) characteristics normally associated with a reciprocating saw of this type The long stroke S (and the speed associated therewith) therefore is greater than that normally associated with saws of this type. This is achieved without any step-up in the capacity of the motor.

A modified form of the invention is illustrated in FIGS. 46. Here, rotary motion of the gear 31 is transferred to reciprocation of the slide 47 by means of the crank 39 which has a pin adapted to pivot and slide laterally in a grooved cross piece 79. In this arrangement, known as :1 scotch yoke, the pivotal and slide connection between the crank 39 and the cross piece 79 eliminates the need for the connecting rod 41 of FIGS. 1-3. Thus, the slide 47 is extended rearwardly and is integral with or otherwise suitably secured to the cross piece 79. In all other respects, the modification of FIGS. 4-6 is the same as that of FIGS. 13 and like numerals refer to like parts.

Another modified form of the invention is illustrated in FIGS. 7-9. Here, rotary motion of the gear 31B is converted into reciprocation of the slide 47 by means of the crank 39B pivoted to the gear 31B by a pin 37, and a connecting rod 41. To achieve the different length strokes (and speeds) of the slide 47, the gear 31B has a shoulder 81 and the crank 39B is formed with a straight edge 83 along one side and a tapered edge 85 along the other side thereof.

When the gear 313 rotates in a clockwise direction, the crank 39B is positioned relative to the gear 31B so that the straight edge 83 engages the shoulder 81 as shown in FIG. 7. In this position of the parts, the slide 47 reciprocates through a stroke equal to twice the radius from the axis of the gear 31B to the pin 43. Conversely, when the gear 31B rotates counterclockwise, the crank edge 83 engages the shoulder 81, as seen in FIG. 8, and the slide 47 now reciprocates through a stroke equal to twice the radius from the axis of the gear 31B to the pin 43 which is somewhat greater than the stroke defined for FIG. 7. In all other respects, the construction of this embodiment is the same as that described for FIGS. 1-3 and FIGS. 46.

By the foregoing, there has been disclosed a novel dual stroke mechanism calculated to fulfill the inventive objects hereinabove set forth, and while a preferred embodiment of the present invention has been illustrated and described in detail, various additions, substitutions, modifications and omissions may be made thereto without departing from the spirit of the invention as encompassed by the appended claims.

I claim:

1. A motion transmission device comprising a first member reversely rotatable about a first axis, a second member pivotally interrelated with said first member and a third member for movement relative thereto about second and third axes, respectively, said first axis being spaced from said second and third axes, means guiding at least a portion of said third member remote from said third axis for reciproctaing movement, cooperable abutment means on said first and second members limiting pivotal movement of said second member relative to said first member, whereby said second member is movable relative to said first member from a first position to a second position, said second member being adapted to pivot to and remain in said first position when said first member rotates in one direction and to pivot to and remain in said second position when said first member rotates in a second direction, whereby said portion of said third member undergoes reciprocational movement having different amplitudes and speeds for rotational movement of said first member in said first and second direction.

2. A device as defined in claim 1 wherein said guide means confines said remote portion of said third member to linear reciprocation.

3. A device as defined in claim 1 wherein said abutment means comprises a pair of projections on said first member, said projections being positioned so that said third axis is spaced different distances from said first axis when said second member is in said first and second positions, respectively.

4. A device as defined in claim 1 which includes a fourth member pivoted to said third member and guided for linear reciprocation toward and away from said first member.

5. A device as defined in claim 1 wherein said second member is pivoted to said first and third members.

6. A device as defined in claim 1 wherein said second member is pivoted to said first member and is pivotally and slidably connected to said third member, said guide means confining said third member for linear reciprocation.

7. A device as defined in claim 1 wherein said abutment means comprises a shoulder on said first member selectively cooperable with said opposite sides of said second member.

8. A reciprocating saw mechanism comprising a housing having a reversible electric motor therein, rotatable means driven by said motor, slide means supported by said housing for longitudinal reciprocating movement and adapted to have a saw blade secured thereto, linkage means within said housing and interconnecting said rotatable means and said slide means, said linkage means being constructed and interconnected with said rotatable means and said slide means whereby to reciprocate said slide means through strokes of different amplitude and speed for forward and reverse motor operation, respectively.

9. A mechanism as defined in claim 8 wherein said linkage means and said rotatable means have cooperable abutment means limiting relative movement between said rotatable means and at least a portion of said linkage means whereby said portion is adapted to move relative to said rotatable means from a first to a second position.

10. A mechanism as defined in claim 9 wherein said linkage means is pivotally interrelated with said rotatable means and said slide.

11. A mechanism as defined in claim 8 wherein said linkage means comprises first and second pivotally interconnected links pivoted to said rotatable means and said slide, respectively, cooperable abutment means on said rotatable means and said first link limiting pivotal movement of said first link relative to said rotatable means, whereby said first link pivots to and remains in a first position relative to said rotatable means during forward motor operation, and pivots to and remains in a second position relative to said rotatable means during reverse motor operation, the interconnection between said first and second links being spaced different distances from the axis of said rotatable means when said first link is in said first and second positions, respectively.

12. A mechanism as defined in claim 9 wherein said abutment means includes spaced projections on said rotatable means cooperable with said linkage means portion.

13. A mechanism as defined in claim 9 wherein said abutment means includes shoulder means on said rotatable means selectively engageable with opposite edges of said linkage means portions.

14. A mechanism as defined in claim 9 wherein said linkage means includes a member pivoted to said rotatable means and pivoted and slidably connected to said blade.

References Cited UNITED STATES PATENTS 6/1925 Hastings 74-44 2/1926 Geddes 74-45 12/1956 Galvez 74-44 5/1964 Wallace 74-44 US. Cl. X.R. 

